Gases, Volume 5, Issue 4 (December 2025) – 8 articles

Global carbon emissions are driving the maritime industry toward cleaner fuels, with LNG already established as a transitional option that reduces SOx, NOx, and particulate emissions relative to conventional marine fuels and in line with decarbonisation strategies. This research aimed to explore the transition of offshore and marine platforms from conventional marine fuels to cleaner alternatives, with liquefied natural gas (LNG) emerging as the principal transitional fuel. Subsequently, floating liquefied natural gas (FLNG) platforms are increasingly being deployed to harness offshore gas resources, yet they face critical challenges related to weight, space, and energy efficiency. The study proposes pathways for transitioning FLNG energy systems from LNG to zero-carbon fuels, such as hydrogen derived directly from LNG resources, to optimise fuel supply under the unique operational constraints of FLNG units. The work unifies the independent domains of pure-fuel and blending-fuel processes for LNG and hydrogen, viewed in the context of thermodynamic processes, to optimise hydrogen–LNG co-firing gas turbine performance and meet the base power line of 50 MW. Furthermore, the research article will contribute to the development of other floating production platforms, such as FPSOs and FSRUs. It will be committed to clean energy policies that mandate support for green alternatives to hydrocarbon fuels. Full article

The aim of this study is to generate density and viscosity data for carbon capture utilization and storage (CCUS) mixtures using equilibrium molecular dynamics (EMD) simulations. Binary CO₂ mixtures with SO₂ and H₂S impurities at mole fractions of 0.05, 0.10, and 0.20 were constructed. Simulations were performed across a temperature range of 223–323.15 K and at pressures up to 27.5 MPa using ms2 software. The simulation results were compared with predictions from established models. These included the Multi-Fluid Helmholtz Energy Approximation (MFHEA) for density, and the Lennard-Jones (LJ), Residual Entropy Scaling (ES-NIST), and Extended Corresponding States (SUPERTRAPP) models for viscosity. Available experimental data from the literature were also used for validation. Density predictions showed excellent agreement with MFHEA, especially for CO₂ + SO₂ mixtures, with %AARD values below 1% for 0.05 and 0.10, and 1.60% for 0.20 mole fraction SO₂. For CO₂ + H₂S mixtures, deviations also increased with impurity concentration, reaching a maximum %AARD of 4.72% at 0.20 mole fraction. Viscosity data were validated against experimental values from the literature for a CO₂ + CH₄ (xCH₄ = 0.25) mixture, showing strong agreement with both models and experiments. This confirms the reliability of the MD approach and the thermodynamic models, even for systems lacking experimental data. However, viscosity estimates showed higher uncertainty at lower temperatures and higher densities, a known limitation of the Green–Kubo method. This highlights the importance of selecting an appropriate correlation time to ensure the pressure correlation functions reach a plateau, avoiding inaccurate or uncertain viscosity values. Full article

The demand for heavy-duty 5% (HD5) propane is expected to increase in the future due to the use of the gas as a fuel for engines. A refinery produces HD10 propane, and it is looking to upgrade to HD5 propane using either the conventional process (distillation) or an energy-saving unit (membrane). This study compared the two technologies in terms of product quality and quantity using process simulation in UniSIM^®. The software also provided the design parameters and power consumption for the two processes. The results show that the membrane was competitive with distillation and was capable of producing 96 mol% propane with a recovery of 99.3%. On the other hand, distillation achieved a maximum propane quality of 95 mol% with a recovery of 99.9%. Surprisingly, the energy consumption in the membrane was 669 kWh, which was higher than that of distillation (540 kWh) due to the requirement for a pre-heating step. Therefore, the technology should be selected based on either the quality or quantity of propane. Full article

Large-scale underground hydrogen storage in saline aquifers requires an understanding of hydrogen–brine two-phase flow properties, particularly relative permeability, which influences reservoir injectivity and hydrogen recovery. However, such hydrogen–brine relative permeability data remain scarce, hindering the predictive modeling of hydrogen injection and withdrawal. In this study, steady-state hydrogen–brine co-injection coreflood experiments were conducted on an Austin Chalk core sample to measure the relative permeabilities. Klinkenberg slip corrections were applied to the gas flow measurements to determine the intrinsic (slip-free) hydrogen permeability. The core’s brine permeability was 13.2 mD, and the Klinkenberg-corrected hydrogen gas permeability was 13.8 mD (approximately a 4.5% difference). Both raw and slip-corrected hydrogen relative permeability curves were obtained, showing that the gas-phase conductivity increased as the water saturation decreased. Gas slippage caused higher apparent gas permeability in the raw data, and slip correction significantly reduced hydrogen relative permeability at lower hydrogen saturations. The core’s irreducible water saturation was 39%, at which point the hydrogen relative permeability reached 0.8 (dropping to 0.69 after slip correction), which is indicative of strongly water-wet behavior. These results demonstrate a measurable impact of gas slippage on hydrogen flow behavior and highlight the importance of accounting for slip effects when evaluating hydrogen mobility in brine-saturated formations. Full article

Emerging technologies such as the Internet of Things (IoT), big data, mobile devices, high-performance computing, and advanced modeling are reshaping urban management. When integrated with conventional tools, these innovations enable smarter governance—particularly in air quality control—improving public health and quality of life. Yet, urban expansion driven by economic growth continues to worsen pollution and its health impacts. This study presents AERQ, a decision support system (DSS) designed to address urban air quality challenges through real-time sensor data and the AERMOD dispersion model. Applied to Cagliari (Italy), AERQ is used to evaluate key traffic-related pollutants (CO, PM, NO₂) and simulate mitigation scenarios. Results are delivered via a user-friendly web-based platform for policymakers, technicians, and citizens. AERQ supports data-driven planning and near real-time responses, demonstrating the potential of integrated digital tools for sustainable urban governance. In the case study, it achieved 10 m spatial and 1 h temporal resolution, while reducing simulation time by 99%—delivering detailed five-year scenarios in just 15 h. Full article

The aim of this study was to rigorously quantify and analyse the concentrations of atmospheric pollutants (PM₁₀, PM_2.5, SO₂, NO₂, CO, H₂S, and O₃) emitted by artisanal brick kilns in Juliaca City, Peru. The AERMOD dispersion model and a network of low-cost sensors (LCSs) were employed to characterise air quality at specific receptor sites. A georeferenced inventory of kiln operations was created to determine their parameters and operational intensity, providing a foundation for estimating emission factors and rates. Data were obtained from the United States Environmental Protection Agency (EPA) and supplemented with locally gathered meteorological records, which were processed for integration into the AERMOD model. The findings revealed that brick kilns are a principal source of atmospheric pollution in the region, with carbon monoxide (CO) emissions being especially pronounced. The LCSs facilitated the identification of pollutant concentrations at various locations and enabled the quantification of the specific contribution of brick production to ambient aerosol levels. Comparative assessments determined that these sources account for approximately 85% of CO emissions within the study area, underscoring a significant adverse impact on air quality and public health. Background pollutant levels, emission rates, spatial distributions, and concentration patterns were analysed within the assessment zones, resulting in solid model performance. These results provide a sound scientific basis for the formulation and implementation of targeted environmental mitigation policies in urban areas and the outskirts of Juliaca. Full article

Carbon dioxide (CO₂), a major greenhouse gas, contributes significantly to global warming and environmental degradation. Carbon Capture, Utilization, and Storage (CCUS) is a promising strategy to mitigate atmospheric CO₂ levels. One widely applied utilization approach involves injecting captured CO₂ into depleted oil reservoirs to enhance oil recovery—a technique known as CO₂-Enhanced Oil Recovery (CO₂-EOR). The effectiveness of CO₂-EOR largely depends on complex rock–fluid interactions, including mass transfer, wettability alteration, capillary pressure, and interfacial tension (IFT). Various factors, such as the presence of asphaltenes, salinity, pressure, temperature, and rock type, influence these interactions. This review explores the impact of these parameters on the IFT between CO₂ and oil/water systems, drawing on findings from both experimental studies and molecular dynamics (MD) simulations. The literature indicates that increased temperature, reduced pressure, lower salinity, and the presence of asphaltenes tend to reduce IFT at the oil–water interface. Similarly, elevated temperature and pressure, along with asphaltene content, also lower the surface tension between CO₂ and oil. Most MD simulations employ synthetic oil mixtures of various alkanes and use tools such as LAMMPS and GROMACS. Experimentally, the pendant drop method is most commonly used with crude oil and brine samples. Future research employing actual reservoir fluids and alternative measurement techniques may yield more accurate and representative IFT data, further advancing the application of CO₂-EOR. Full article

Gasification of residual biomass has emerged as an efficient thermochemical conversion process, applicable to a wide range of uses, such as electricity generation; chemical manufacturing; and the production of liquid biofuels, BioSNG (biomass-based synthetic natural gas), and hydrogen. Thus, gasification of biomass residues not only constitutes an important contribution toward decarbonizing the economy but also promotes the efficient utilization of renewable resources. Although a variety of gasification technologies are available, there are no clear guidelines for selecting the type of gasifier appropriate depending on the feedstock and the desired downstream products. Herein, we propose a gasifier classification model based on an extensive literature review, combined with a multi-criteria decision-making approach. A comprehensive and up-to-date literature review was conducted to gain a thorough understanding of the current state of knowledge in biomass gasification. The different features of the different types of gasifiers, in the context of biomass gasification, are presented and compared. The gasifiers were reviewed and evaluated considering criteria such as processing capacity, syngas quality, process performance, feedstock flexibility, operational and capital costs, environmental impact, and specific equipment features. A multi-criteria classification methodology was evaluated for assessing biomass gasifiers. A case study of such methodology was a applied to determine the best gasifiers for BioSNG inclusion in the natural gas distribution system in a small-scale scenario. Validation was conducted by comparing the matrix findings with commercially implemented gasification projects worldwide. Full article