Methane, Volume 3, Issue 2 (June 2024) – 8 articles

This study investigates the utilization of controlled nanocatalysts in methane conversion reactions, addressing the pressing need for the efficient utilization of methane as a feedstock for valuable chemicals and clean energy. The methods employed include a comprehensive review of recent advancements in nanocatalyst synthesis, characterization, and application, as well as the critical analysis of underlying mechanisms and controversies in methane activation and transformation. The main findings reveal significant progress in the design and synthesis of controlled nanocatalysts, enabling enhanced activity, selectivity, and stability in methane conversion reactions. Moreover, the study highlights the importance of resolving controversies surrounding metal–support interactions for rational catalyst design. Overall, the study underscores the pivotal role of nanotechnology in shaping the future of methane utilization and sustainable energy production, providing valuable insights for guiding future research directions and technological developments in this field. Full article

In the present study, a comparison of the dry reforming of a gas mixture containing methane, carbon dioxide and nitrogen without contaminants to a ruthenium-based Ru/Al₂O₃ catalyst was carried out in a microreactor for the first time. The influence of the contact time, temperature and composition of the feed on the conversion was exhaustively investigated. The optimal operating conditions were found to be a contact time of 80 milliseconds, a temperature of 700 °C and a CH₄:CO₂ ratio of 1. The assessment of diffusional limitations reveals that there is no resistance to mass transfer, which reveals the potential benefit of the determination of intrinsic reaction kinetics within a microreactor. Full article

To solve the sand problem during the depressurization of methane hydrate (MH), we proposed a method to build a porous grout body with sufficient permeability and strength around the wellbore through inhibitor pre-injection and grouting, and verified its effectiveness and potential in our previous research using artificial cores created with silica sand and alternative hydrates such as TBAB- hydrate and iso-butane hydrate. However, all of the artificial cores mentioned above were created with high homogeneity, injected, cured, and had their physical properties measured in the vertical direction, which differs from real reservoir conditions. To investigate the effects of grouting in a more realistic fluid flow, we conducted further experiments using horizontal 1D cores, 1D cubic models, and a 2D cross-sectional model mimicking the near wellbore. These experiments revealed that (1) the generated gas somewhat suppressed the effects of grouting as in the case of previous experiments, and (2) grouted reservoirs would be heterogenous and anisotropic due to the fluid densities and the distribution of grout particles and turbidite sediments, but sufficient permeability and satisfactory strength could still be attained. The above series of experiments demonstrated that our method has the potential to effectively produce actual MH, preventing sand problems even in heterogeneous and anisotropic grouted reservoirs. Full article

This study mapped the bioenergy production from sugarcane vinasse according to the mesoregions of the State of São Paulo (SP), Brazil, assessing the magnitude of biogas-derived electricity and biomethane production and estimating the greenhouse gas (GHG) emissions. SP holds 45% of the Brazilian ethanol-producing plants, in which 1.4 million m³ of carbon-rich vinasse are generated daily. The electricity generated from vinasse has the potential to fully supply the residential consumption (ca. 6.5 million inhabitants) in the main sugarcane-producing mesoregions of the state (Ribeirão Preto, São José do Rio Preto, Bauru, Araçatuba and Presidente Prudente). In another approach, biomethane could displace almost 3.5 billion liters of diesel, which represents a 26% abatement in the annual state diesel consumption. Energetically exploiting biogas is mandatory to prevent GHG-related drawbacks, as the eventual emission of methane produced under controlled conditions (261.2 × 10⁶ kg-CO₂eq d⁻¹) is ca. 7-fold higher than the total emissions estimated for the entire ethanol production chain. Meanwhile, replacing diesel with biomethane can avoid the emission of 45.4 × 10⁶ kg-CO₂eq d⁻¹. Implementing an efficient model of energy recovery from vinasse in SP has great potential to serve as a basis for expanding the utilization of this wastewater in Brazil. Full article

The role of methane (CH₄) in the 21st century presents a critical dilemma. Its abundance and clean-burning nature make it a promising energy source, while its potent greenhouse effect threatens climate stability. Despite its potent greenhouse gas (GHG) nature, CH₄ remains a crucial energy resource. However, advancements in CH₄ capture, utilization, and emissions mitigation are rapidly evolving, necessitating a critical assessment of the advances, their potential, and challenges. This study aims to comprehensively evaluate the current state of the art in these advancements, particularly focusing on the emissions trends, with corresponding global warming potentials of projected CH₄ emissions, and a discussion on the advances that have been made towards reducing the impacts of CH₄ emissions. The areas of these advances include measurement, computational, numerical modeling, and simulation studies for CH₄, emerging technologies for CH₄ production, management and control, the nexus of CH₄ –X, and case study applications in countries. This study reports on these advances, which involves a technical review of studies, mainly from the last decade, discussing the technical feasibility, economic viability, and environmental impact of these advancements. Our trend analysis reveals that even though the share of CH₄ in the GHG mix has been around 19% compared with carbon dioxide (CO₂), still, CH₄ reduction would need to be highly subsidized because of the high global warming potential it has, compared with CO₂. We conclude that while significant progress has been made, further research and development are essential to optimize the performance, scalability, and affordability of these advancements. Additionally, robust policy frameworks and international collaborations are crucial to ensure widespread adoption and maximize the potential that comes with the advancements in the mitigation of the impact of CH₄ emission. This study contributes to the ongoing dialogue on balancing the potentials of CH₄ with its environmental footprint, paving the way for a future where this versatile resource can be utilized sustainably. Full article

Saprotrophic fungi, key players in global carbon cycling, have been identified as methane (CH₄) sources not yet accounted for in the global CH₄ budget. This study, for the first time, explores the influence of oxygen (O₂) and temperature on CH₄ production by two fungi, Laetiporus sulphureus and Pleurotus sapidus. To explore the relationship between these parameters and fungal CH₄ formation, we examined CH₄ formation under varying O₂ levels (0 to 98%) and temperatures (17, 27, and 40 °C) during fungal growth on pine wood, beech wood, and grass under sterile conditions. Our findings show that fungal CH₄ formation strongly depends on O₂ levels. Methane formation was highest when O₂ levels exceeded 5%, whilst no CH₄ formation was observed after complete O₂ consumption. Reintroducing O₂ immediately resumed fungal CH₄ production. Methane formation normalized to O₂ consumption (CH₄__norm) showed a different pattern. L. sulphureus showed higher CH₄__norm rates with higher O₂ levels, whereas P. sapidus showed elevated rates between 0 and 5%. Temperature also significantly influenced CH₄ and CH₄__norm rates, with the highest production at 27 °C, and comparatively lower rates at 17 and 40 °C. These findings demonstrate the importance of O₂ levels and temperature in fungal CH₄ emissions, which are essential for refining CH₄ source predictions. Full article

Low and unstable digestion performance is a challenging issue for anaerobic digestion, which prompts researchers to develop new strategies. In addition to traditional approaches such as co-digestion, pre-treatment, and recirculation, some emerging strategies, namely additive processes and microaeration, have also been recognized and developed in recent years. Many studies have evaluated the effect of these strategies on digestion performance. However, their comprehensive analysis is lacking, especially regarding the mechanisms of the different strategies. This review presents a comprehensive overview of research progress on these strategies based on the latest research, considering the five main strategies listed above. Through critical thinking, a summary of their mechanism, reactor performance, and availability of these strategies is presented. The results demonstrate that the contribution of microaeration is mainly to balance the composition and activity of hydrolysis, acidogenesis, and methanogenic archaea. Recirculation and co-digestion mainly balance mass and reaction environments. Pre-treatment, such as removing lignin, reducing cellulose crystallinity, and increasing the substrate-specific surface area, makes the characteristics of the substrate more conducive to the digestion of microorganisms. The mechanism of additive strategies varies greatly depending on the type of additive, such as enhancing interspecies electron transfer through conductive materials, resisting adverse digestion conditions through functional microbial additives, and accelerating nutrient absorption by regulating the bioavailability of trace elements. Although these strategies have different mechanisms for promoting digestion performance, their ultimate effect is to allow the parameters of the reactor to reach an ideal status and then achieve a balance among the substance, microorganisms, and water in an anaerobic reactor. Full article

Psychrophilic anaerobic digestion emerges as an appealing integrated solution for the management of agricultural waste, particularly for farmers in regions where the average temperature does not exceed 26 °C, as seen in coffee cultivation. Therefore, this study seeks to assess the biomethane potential of thermochemical-treated coffee husk through psychrophilic anaerobic digestion (C3-20 °C-w/pretreatment). To examine its viability, outcomes were compared with reactors operating at both mesophilic (C1-35 °C) and psychrophilic (C2-20 °C) conditions, albeit without the use of pretreated coffee husk. The C3-20 °C-w/pretreatment test demonstrated a 36.89% increase (150.47 NmL CH₄/g VS; 161.04 NmL CH₄/g COD), while the C1-35 °C test exhibited a 24.03% increase (124.99 NmL CH₄/g VS; 133.77 NmL CH₄/g COD), both in comparison to the C2-20 °C test (94.96 NmL CH₄/g VS; 101.63 NmL CH₄/g COD). Notably, the C3-20 °C-w/pretreatment trial yielded superior outcomes, accompanied by an associated energy output of 3199.25 GWh/year, sufficient to meet the annual energy demands of 494 residences. This marks an increase of 83 and 182 million residences compared to the mesophilic and psychrophilic AD of CH without pretreatment, respectively. Full article